With respect to current image display systems, such as CRTs, PDPs and liquid crystal displays, attempts have been rapidly made to make the display portions thinner or flat.
However, since the display portions per se are not transparent, the display portions per se are unpleasant to the eye or give a feeling of oppression to a viewer when the display portions are active and even when the display portions are not active. For these reasons, it has been demanded to provide a display portion, which can turn transparent so as to give a feeling of expansion to a viewer and allows the viewer to see a scene behind the display portion.
As one of the solutions, there is, e.g., a display system called a head-up display for a car. This is a method wherein an image projected from an image-projecting unit is reflected by a half-mirror provided on a windshield or by a hologram system whereby the image looks like being displayed on the windshield. In this method, since the half-mirror or the hologram system is not completely transparent when no image is displayed, the half-mirror or the hologram system is visible and unpleasant to the eye.
There is also a display system, which uses a hologram screen to provide attractive display in, e.g., a show window at a shop. In this system, light that enters a hologram screen from a projector at a particular angle is scattered on the hologram screen to display an image. This system can display an image having a high contrast since light that enter at angles other than the particular angle is not scattered. However, when a viewer is located at an oblique position to the screen, the viewer cannot see an image since this system has a narrow viewing angle because of a viewing angle dependency.
JP-U-04-114088 has disclosed an image display system, which uses a single screen as the transparent member, and which switches the screen from a light transmissive state to a light scattering state or vice versa (see the abstract and FIG. 1). This system can not realize a state with an image displayed in a background scene since the screen is not transparent while displaying the image.
On the other hand, JP-A-05-191726 has disclosed a technique to realize a state with an image displayed in a background scene (see paragraph number 0010 and FIG. 1). This technique brings only a portion to display an image into a scattering state to use that portion as a screen. When the image is displayed, it is not possible to see a scene behind the image. This publication is silent about a technique to use a plurality of screens.
The technique to use a plurality of screens has been disclosed in JP-A-05-307185 (see paragraph numbers 0020 and 0021, and FIGS. 4 and 5). This publication is silent about an idea of allowing a viewer to see a background scene.
Additionally, JP-A-2002-139700 has disclosed a technique, which displays a three-dimensional image on a screen comprising a plurality of liquid crystal cells (see paragraph numbers 0019 to 0021, and FIGS. 1 and 2). This publication is also silent about an idea of allowing a viewer to look a background scene.